In standard CMOS devices, polysilicon is typically the standard gate material. The technology of fabricating CMOS devices using polysilicon gates has been in a constant state of development, and is now widely used in the semiconductor industry. One advantage of using polysilicon gates is that they can sustain high temperatures. However, there are also some problems associated with using a polysilicon gate. For example, due to the poly-depletion effect and relative high electrical sheet resistance, polySi gates commonly used in CMOS devices are becoming a gating factor in chip performance for channel lengths of 0.1 micron and below. Another problem with polySi gates is that the dopant in the polySi gate, such as boron, can easily diffuse through the thin gate dielectric causing further degradation of the device performance.
In order to avoid the problems with polySi gates, it has been suggested to replace the polySi gate with a single metal. Although such technology has been suggested, single metals are not thermally stable on a high k (dielectric constant greater than about 4.0)/interfacial layer gate stack. For example, tungsten, W, and rhenium, Re have stability problems at 1000° C. Tungsten shows interfacial SiO2 regrowth at 4-5 Å after 1000° C., 5 second anneal limiting device scaling and Re is not stable on a high k gate stack, leading to device (mobility) degradation. See, for example, A. Callegari, et al., IEDM 2004, p. 825, S. Francisco Calif., Dec. 13-15, 2004 and Narayanan, et al., VLSI Digest 2004, Hawaii June 2004.
Stability at 1000° C. is required to activate the source/drain implant in self-aligned metal oxide semiconductor field effect transistors (MOSFETs). Also, it has been reported that high electron mobilities are obtained when performing a high temperature anneal. See, for example, A. Callegari, et al., IEDM 2004, p. 825, S. Francisco Calif., Dec. 13-15, 2004. Metal nitrides such as TiN have been extensively used to improve the metal/high k thermal stability. However, most of the work reported on TiN shows that TiN is a mid-gap material which may have limited device performance.
Co-assigned and co-pending U.S. patent application. Ser. No. 11/034,597, filed Jan. 13, 2005 describes TiC as a possible solution for the above-mentioned problem. While metal carbides are electrically stable at 1000° C. and pFET behavior is maintained, carbon diffusion may occur in the interlayers which may, in turn, contribute to carbon contamination.
In view of the above, there is a need for providing a new compound metal which is thermally stable on a gate stack including a high k dielectric which does not cause carbon diffusion as may be the case with metal carbides. In particular, there is a need for providing a new compound metal useful in pFET devices.